eXtplorer - PHP-based File Manager

eXtplorer not loading in Joomla

Thanks for eXtplorer. I use it on all of my sites.I have been having difficulty getting it to run on a couple of sites. I get the same error: The header info (Back to Joomla!, eXtplorer logo, mode message) shows up twice, and eXtplorer never loads. See attached screenshot.

Both sites are for the same client. The old site was Joomla 1.5 The second site is J3.6 with eXtplorer 2.1.9. Any suggestions on how to fix this?